The invention relates to a wheel for motor vehicles, of the type which is cast or forged in one piece, and composed, in particular, of a light metal alloy, this wheel possessing a rim and a wheel disc, a radial clearance being present between the periphery of the wheel disc and the rim, which clearance is bridged by connecting webs.
Motor vehicle wheels of the design described above are already known (German Offenlegungsschriften 1,802,298 and 2,853,606).
The above-mentioned publications are concerned with designs in which the radial clearance between the wheel disc and the rim is utilized in order to form air exit apertures, which are located between the connecting webs, and through which streams of air can flow away, this flowing air serving to cool the disc brake which is installed in the region of the wheel disc. For this purpose, the connecting webs on the rear surface of the wheel disc, and, if appropriate, on its front surface, extend radially inwards and function in conjunction with the wheel disc in the manner of a radial fan.
In these known embodiments, the forces which become active at the wheel are transmitted via the connecting webs into the wheel rim as the vehicle is driven under power, or are transmitted into the wheel disc when the vehicle is being pushed, it being necessary to design the wheel disc and/or the connecting webs with appropriate dimensions so as to achieve the necessary strength.
Moreover, motor vehicle wheels possessing the features of the design referred to above also belong to the state of the art, a fact which cannot be substantiated by means of publications, but which is known from practice, in which designs the connecting struts extend merely between the external periphery of the wheel disc and the internal periphery of the rim in the region of a rim-bead.
This design necessitates that the wheel disc be designed with appropriately generous dimensions, in order to ensure that the connecting webs are equally stressed. This requirement, however, conflicts with efforts, prompted by reasons of cost, to reduce the amount of material required for the wheels, and especially for wheels composed of expensive light metal alloys. An object on which the invention is based is accordingly, on the one hand, to make it possible to produce wheel discs which are, at least locally, considerably thinner and, on the other hand, to bring about a further increase in the stiffness of wheels of this type, as a result of a detail-improvement in their construction.
These objects are achieved according to the invention by means of a design wherein a stiffening ring, extending both peripherally and axially, is moulded onto the inner surface of the wheel disc, and the connecting webs are moulded onto the outer, annular surface of the stiffening ring, this surface forming the peripheral surface of the wheel disc.
Furnishing the wheel disc with a stiffening ring, which is moulded onto the disc in its peripheral zone, ensures that the wheel is stiffened to the extent necessary for equal stressing of the connecting webs, even in cases where the wheel disc is of comparatively thin-walled design.
In the axial direction, the stiffening ring can extend up to a front end-wall portion of the rim, and can if appropriate, merge integrally into this end-wall portion, in which case the wheel possesses no window-like apertures. The wheel will preferably be furnished with apertures of this nature in order to enable streams of air to form as the wheel rotates, these streams of air being drawn off via these apertures for the purpose of cooling the brakes. For this purpose, the stiffening ring must be designed in a manner such that openings are made in it, in the radial direction, between the connecting webs. This presupposes that the connecting webs extend to the front end-wall portion of the rim. However, it is also contemplated to design the stiffening ring in a manner such that it is shortened in the axial direction, so that a clearance extending in the peripheral direction is present between this ring and the front end-wall.
An object which is to be achieved by means of the invention relates more specifically to the further development of an internally-ventilated wheel, in which the connection of the ventilation passages, present between the connecting webs, to the wheel interior is invisible when the wheel is viewed from the front, the purpose of which is to produce a wheel having a front, outside face possessing a shape which is particularly outstanding in aesthetic terms, while the outer surface of this wheel is less extensively soiled by the brake-friction material which is rubbed off during braking, and is distinguished by high strength, deriving from its shape, despite the fact that its design leads to a saving in materials.
This object is achieved by means of disposition of the openings forming the exit apertures of the ventilation passages, with these apertures being directed into the wheel interior so that they do not, due to the fact that they run radially, fall into the field of view. The stiffening ring produces the desired additional stiffening of the wheel disc, thus enabling it to be designed with a particularly thin wall. In addition, the stiffening ring forms on the wheel disc an appropriately dimensioned connection-base for the connecting webs. Finally, a portion of the brake friction-material which is rubbed off during braking can, under the influence of inertia, deposit on the inner periphery of the stiffening ring, and is consequently prevented from escaping at the ventilation apertures.
In terms of foundry technology, it is possible to produce the arrangement embodying apertures along the periphery of the stiffening ring, extending radially, but the production of such a casting necessitates that the mould be equipped with appropriate gates which can be moved radially, or with other adequate devices which complicate the construction of the mould and render it correspondingly more expensive. Equipping the mould in this way can be avoided by conventionally machining a cast wheel, in which, in accordance with the above proposal the connecting webs extend in the axial direction up to the front end-wall portion of the rim. This machining operation must be carried out on the internal periphery of the stiffening ring and, in particular, this operation necessitates the machining of an annular slot into the inner peripheral surface of the stiffening ring, this slot finally breaking through the ring in the radial direction, so that in the end the wheel disc is connected to the rim only via the connecting webs which remain intact. This measure is regarded as a manufacturing process which is independently worthy of patent protection within the scope of the present invention.
In addition, the machining procedure for the production of window-like air exit apertures as described above permits the front, outside face of the wheel to be given an unusual shape, in that the apertures which can be produced by the conventional machining operation adjoin the annular, outside face of the stiffening ring produced by this operation in the axial direction and consequently open radially into the interspace between the wheel disc, or, as the case may be, the stiffening ring, and the rim. Insofar as the rim is of the type which is furnished with a deep base, it is advantageous with regard to the machining operation on the stiffening ring as explained, to arrange the inner peripheral surface of the stiffening ring and the inner peripheral surface of the deep rim base, one with respect to the other, in a manner such that they lie on a common shell surface. Before the machining operation, the two inner peripheral surfaces thus form a continuous inner peripheral surface of the wheel, enabling undercutting to be avoided during casting or forging. At the same time, optimal flow of the materials from the stiffening ring to the rim is achieved, especially for a wheel which is manufactured by casting.
In the case of a wheel which possesses window-like apertures, arranged as explained between the connecting webs which join the wheel disc to the rim, the stiffening ring on the wheel disc brings about the additional advantage that the rubbed-off brake friction material produced during braking can deposit, under the influence of inertia, on the internal periphery of the stiffening ring, as a result of which soiling of the outer surface of the wheel is correspondingly reduced.
These and further objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.